I have several servers in different datacenters with public ip addresses assigned, think of ovh etc. There is no better solution for public containers than OVZ7, that is a fact.
I am stuck on migrating containers between the datacenters.

VZMigrate
vzmigrate is deprecated.
-r, --remove-area no = no longer works, the container is deleted after the migration..

OVZ Migrate
ovzmigrate.sh is for container migration from virtuozzo 6 to virtuozzo 7+ and works, but is this the official way for OVZ7 to OVZ7?

Results with firewall disabled:
Failed to migrate the VM: Unable to establish a connection between "x.x.x.x" and "ovz7.xx.com". The network connection between these servers may be broken, or one of the servers may be down. Contact your Virtuozzo administrator for assistance.

i think there is still something with firewall.
i'd start with disabling firewall completely, putting sshd on default 22 port and attempt to migrate.
If it works, move sshd on same port on both nodes, say, 2222 and retry.
If it works, move sshd on one node on a different port like you have now and try again.

Hope that helps.

If you problem is solved - please, report it!
It's even more important than reporting the problem itself...